The present invention relates to a torque converter in which a bell-shaped casing shell rotatably accommodating a centripetal-flow turbine wheel is connected in a pressure-tight manner to the outer shell of a pump impeller and to the turbine wheel to move therewith, by way of a lock-up clutch which, can be actuated by a clutch actuator of the axial piston type, and in which the friction discs of the lock-up clutch are alternatively torsionally held on two annular friction disc carriers which are concentric with the torque converter axis of rotation.
In a known torque converter of the type mentioned in British Patent Specification 1,485,085, the friction discs are arranged in a chamber encapsulated against the pressure medium by the solid friction disc carrier, the solid abutment disc and the solid axial piston so that difficulties arise with respect to the removal of heat when the lock-up clutch is engaged.
An object on which the present invention is the creation of interference-free heat removal so as to ensure a sensitive, accurately metered control of the clutch slip of the lock-up clutch, with this control being intrinsically used for fuel economy. By regulating a certain slip condition, the transmission of torque non-uniformities of the drive engine to the drive train downstream of the torque converter in the force path is also prevented.
The foregoing object has been achieved in an advantageous manner in accordance with the present invention by providing that a coupling space is provided within the casing, which coupling space is bounded in one direction of the torque converter axis of rotation by a radial end wall of the casing shell and, in the opposite direction by the turbine wheel, the clutch space has, at a radially outer position, a flow connection to an annular gap between the pump impeller outlet and the turbine wheel inlet and, has at a radially inner position, a flow connection to a torque converter return conduit, and the friction disc carriers provided with radial through-flow openings are arranged so that their complete length is located transversely in the centrifugal flow of the clutch space occurring between the two flow connections.
In the torque converter according to the present invention, the influence of heat generated by frictional work on the control of the clutch slip is kept small because the friction discs are arranged in an outer cooling oil flow branched off from the annular gap between the pump impeller outlet and the turbine wheel inlet.
In the torque converter according to the invention, providing oil delivery grooves on the ends of the friction discs held in a carrier also contributes to intensifying the cooling oil flow through the lock-up clutch. The effect of a centripetal flow through the lock-up clutch is amplified by providing that the second flow connection contains at least one axial through-hole of the wheel hub of the turbine wheel.
In the torque converter according to the present invention, the pressure level can be kept low in the case of a clutch actuation and thereby the sealing of the pressure passages can be facilitated if the friction discs are arranged axially between an abutment, held so that as to be fixed axially and so held torsionally on one of the friction disc carriers and an annular pressure piece, and at least one transmission lever is operatively arranged between the pressure piece and the axial piston to increase a resultant engagement force on the pressure piece relative to the piston pressure force is effectively arranged, the pressure piece being held so as to be axially displaceable and torsionally fixed on the friction disc carrier having the abutment. The rotational speed range in which the transmission of rotational vibrations of the drive engine to the downstream drive train is avoided and is substantially extended where the casing shell is connected to the turbine wheel by a torsional vibration damper arranged in series in a force path with the lock-up clutch and connected to one of the friction disc carriers.